While basic allocation sets the base size of your buffer pools, dynamic expansion enables a buffer pool to be expanded temporarily during periods of heavy demand. Its use can greatly increase the efficiency with which VTAM uses storage, particularly for I/O buffers.

Without dynamic expansion of a pool, basic allocation parameters must be specified large enough to meet the greatest possible demands on the pool. With dynamic expansion, smaller basic allocation values can be specified, and peak demands on the pool can be met with dynamic expansion. Dynamic expansion is strongly recommended for most buffer pools because the peak demand can vary considerably from the normal demand.